Digital image capturing devices, such as digital cameras and camcorders, include an optics assembly that directs light from an object onto an image sensor formed by an array of photo sensors arranged in rows and columns. Each of the photo sensors detects the light incident upon that sensor and in response to the detected light the sensor develops an electric charge. In this way, the light from different portions of an image is detected by corresponding photo sensors in the array and the sensors convert the detected light into corresponding electric charges. The stored electric charge in each photo sensor generates a voltage and the device then performs an analog-to-digital conversion to convert the voltage in each sensor into a corresponding digital value. The digital values for each of the sensors collectively form a digital image file that represents the captured image. Each of the photo sensors may sometimes be referred to as a picture element or “pixel” in the following description.
During the capturing of an image, the photo sensors in the array must be exposed to light from the object being imaged for a sufficient amount of time. This time is commonly referred to as an “exposure time” and must have a duration that allows each sensor to develop a sufficient charge which, in turn, develops a voltage having a sufficient magnitude to allow reliable conversion of this analog voltage to a corresponding digital value. In a digital camera this time may be termed an “exposure time” and is set by a shutter that opens and closes. The shutter opens to allow light to propagate through the optics assembly and thereafter closes to block any further light from being incident upon the photo sensors in the array. The time between when the shutter opens and closes is the exposure time.
While the shutter is open, the digital camera or other image capturing device is ideally held perfectly still so that light from given portions of an image is incident upon the same photo sensor in the array. For example, assume the image sensor is formed by a 1024×1024 (1024 rows by 1024 columns) array of photo sensors. During the capture of an image, light from a certain portion of the object being imaged will propagate through the optics assembly and be directed onto corresponding photo sensors in the array. Assume light from the upper right portion of the object is incident upon photo sensors in the upper left portion of the array, with these photo sensors or pixels being designated as P11 to P55 as shown in FIG. 1. The first number in the subscript indicates the row of the pixel within the array and the second number the column of the pixel. FIG. 1 thus shows a 5×5 array of the pixels P11 to P55 in the upper left portion of the image sensor.
Assume at the start of the exposure time that light forming an image of a small arrow is incident upon the pixels in column three P13 to P53 along with the pixels P22 and P24. This light results in a unit of charge C accumulating in each of the pixels P13–P53, P22 and P24. Now assume that during the exposure time, the digital camera is moved by a user of the camera such as may occur when a user depresses a button on the camera to take a picture. Because of this motion, assume that the light forming the image of the arrow is now shifted to the right one pixel as illustrated by an arrow 100 in FIG. 1. The light is then incident upon pixels P14–P54, P23 and P25, which results in an additional charge C accumulating in each of these pixels. Light is incident on the pixels P23 and P24 even after the movement and thus each of these pixels accumulates a charge 2C, which is indicated as two Cs in FIG. 1. Assume the shutter of the camera closes at this point, terminating the exposure time so that the charge on each of the pixels P11 to P55 is as shown in FIG. 1.
FIG. 1 illustrates that due to the movement of the digital camera during the exposure time, the charge accumulated in the pixels P11 to P55 is spread among more pixels than would otherwise be the case if no such movement had occurred. This phenomenon is sometimes referred to as “motion induced blurring.” The image being capture is “blurred” in that the image is now spread over more pixels than would ideally be the case if no such movement had occurred. Without any movement each of the pixels P13–P53, P22, and P24 would accumulate the charge 2C in the example of FIG. 1. Due to the movement, however, this charge is now spread among additional pixels.
Conventional digital image capturing devices like digital cameras utilize a variety of different types of image stabilization systems to compensate for motion induced blurring. The image stabilization system includes a motion sensor that detects movement of the camera in a given direction. Typically the motion sensor is either an accelerometer that detects acceleration of the camera in various directions or a gyroscope that detects movement of the camera in such directions. In response to the detected movement of the camera, the stabilization system controls the optics assembly in the camera to correct for the movement of the camera. The optics assembly corrects for such movement by redirecting light propagating through the optics assembly such that the light continues to be incident on the same pixels in the array after the movement as before the movement. For example, referring to FIG. 1 the image stabilization system controls the optics assembly to redirect the light such that the light is incident upon the pixels in column three P13 to P53 along with the pixels P22 and P24 during the entire exposure time.
These conventional image stabilization systems typically control the optics assembly in one of two ways to compensate for camera movement. First, the optics assembly may include two lenses that are optical complements of one another such that the system moves one of these lenses relative to the other to thereby redirect the light, as will be understood by those skilled in the art. Another approach places a flat piece of glass in the propagation path of the light and rotates this piece of glass to redirect the light due to the change in refraction of the light passing through the glass as the glass is rotated. Both types of image stabilization systems are mechanical systems in that components in the optics assembly are being physically moved to compensate for movement of the camera. As a result, such systems are prone to failure as components wear out or fail. In addition, the size and mass of components being controlled limits the speed of operation of these image stabilization systems. This may result in unwanted motion induced blurring due to the response time of the image stabilization system being too slow to compensate for some types of movements.
There is a need for an image stabilization system having a reduced rate of failure and improved response time to compensate for a wider range of movements.